The present invention relates to a read/write amplifier circuit of a magnetic disk unit and more particularly to a read/write circuit of a hard disk unit.
In the conventional read/write amplifier, an output of the read signal other than the reading on time is performed by the read signal output of a high impedance or an output of a constant DC current bias for the read signal output.
The conventional read/write amplifier circuit of the type mentioned has some defects to be described hereinafter with reference to FIGS. 2 and 3.
On FIG. 2, the conventional circuit has the first, second and third read/write amplifiers 27, 28 and 29, the first, second and third head coils 30, 31 and 32, the read/write switch signal input terminal 21, the first, second and third chip select input terminals 22, 24 and 26, the read signal output terminal 23, and the write data input terminal 25. The first, second and third read/write amplifiers 27, 28 and 29 each provides two amplifiers as shown in FIG. 3.
In the arrangement where the DC bias is output for the read signal output other than the read on time, when two or more read/write amplifiers are connected together as shown in FIG. 2, the DC bias is outputted even from the read signal of the unselected read/write amplifier, so that two read/write amplifiers could not be connected together.
Further, in the arrangement, the read signal output is a high impedance other than at the reading on time. An automatic gain control (hereinafter referred to as AGC) in the next stage has an extended setting-time, for example, at the time of transision from a write mode to a read mode.
The problem hereinbefore described is attributed to operation of the AGC circuit responsive to the DC voltage variation or the DC voltage difference caused when returned to the status during a read time since charges stored in the first capacitor 31 and the second capacitor 37 are discharged by the input resistor 38 of the AGC amplifier 35 when the read amplifier 34 provides a high impedance output due to the connection of the read amplifier 34 with the AGC amplifier 35 through the first and second capacitors 36 and 37 as will be appreciated from FIG. 3.
The head coil 33 is connected to the read amplifier 34, and the output 39 of the AGC amplifier is outputted from the AGC amplifier 35.